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arity with geological subjects, to offer some suggestions respect- 

 ing the upper series of the blufF formation itself. 



The most remarkable portion of this formation is the upper 

 bed, or that next below the soil of the surface. It consists of a 

 yellowish calcareous loam, thickly filled in many places with ter- 

 restrial shells, and in others, with a few fluviatile species. The 

 depth or thickness of this bed is described to be from twenty to 

 fifty feet. The material of which it is composed is minutely 

 comminuted, and, when dried, falls into an impalpable powder. 

 The shells are generally unbroken, the most delicate edges of the 

 aperture remaining entire, and, except in the loss of color, and 

 the want of cohesion caused by the destruction of their animal 

 matter, they are precisely similar to existing species. The calca- 

 reous concretions and bones, found in this bed, are also mostly 

 unbroken, and exhibit no marks of friction, or wear, in a current 

 of water. The condition of the bed, and of its contents, seems, 

 therefore, to forbid the opinion that they ever formed a part of a 

 great diluvial current, but point rather to a slow subsidence of 

 the materials in still water. Under any other circumstances, the 

 minute particles would have been mixed with other matter, and 

 the shells, some of them of a thin and delicate texture, would 

 have been mostly fractured and crushed. 



Below the loam, is a bed of light ash-colored marl, containing 

 fluviatile shells, and having a thickness of from five to ten feet ; 

 this, with only an intervening stratum of fine gravel, is succeeded 

 by a bed of sandy loam, from twenty to thirty feet in thickness, 

 containing bones of the mastodon. The other deposits are mostly 

 clays and sands, with calcareous and arenaceous concretions, and 

 limonites, of too soft a consistence, and too loose a structure, 

 ever to have withstood the grinding and wearing effects of a rapid 

 motion in a stream of sand and water. At the depth of one 

 hundred feet, or thereabouts, (for it has not been accurately 

 measured,) there occurs a stratum of two and a half to three 

 feet in thickness, of rolled and water-worn fragments of agate, 

 calcedony, cornelian and hornstone, with agatized corals, madre- 

 pores and encrinites, having precisely the appearance they might 

 be supposed to have if brought down, by the current, from the 

 upper districts of the river. Below these, clays and sands, with 

 concretionary minerals, fossilized wood, and lignites, imbedded 



